Micelle Formation of Protic Ionic Liquids in Aqueous Solution - Journal

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Micelle Formation of Protic Ionic Liquids in Aqueous Solution Dheiver Santos* Department of Engineering, Tiradentes University Center (UNIT), Av. Comendador Gustavo Paiva, 5017, Cruz das Almas, Maceió, Alagoas, CEP: 57038-00, Brazil Department of Engineering, Maurício de Nassau University Center (UNINASSAU), R. José de Alencar, 511 - Farol, Maceió, Alagoas, CEP: 57051-565, Brazil S Supporting Information *

ABSTRACT: The ionic liquids potentialities to organize themselves in aqueous solution and produce aggregates were analyzed through the conductivity technique and after using a new mathematical model based on stochastic theories, to indicate the linearity change moment; it was possible to analyze the presence of these aggregates. It earns interest at science of colloids and interfacial chemistry due to the recognized ability of certain surfactant ionic liquids to reduce the surface tension of aqueous solutions and to aggregate in the form of micelles, even at low concentrations, allowing their use as stabilizing or destabilizing agents in homogeneous polymerization in water/oil emulsions. Within this context, this work aims to verify the possible micellar properties of the ionic liquids. Critical micellar concentration values for ions ammonium alkyl carboxylates were obtained. It was also shown that the CMC is directly related to the lipophilic groups of the cation and entropic factors. were consistent with the formation of micelles. Santos et al.4 observed the formation of aggregates via ionic liquids based on the conductivity measurement with anion stearate. Therefore, the self-aggregation study and surface interactions are essential in understanding properties, technical applications, and the environmental fate of ILs. Santos et al.17 was showed that the electric conductivity of aqueous solutions of protic ionic liquids based on stearates decreases with the increase of anion and the side-chain size, the authors reveal that this behavior is related to the fact that the medium becomes more organic which causes the conductivity to decrease. In other works, it has frequently been observed that ionic liquids are used as inhibitors of gas hydrates.18,19 Alcantara et al.20 reported the vapor−liquid equilibrium data of systems composed by CO2 + protic ionic liquid to predict the carbon dioxide activity coefficients. They suggested that the boiling point elevations depend on the interaction forces between carbon dioxide and ionic liquids because of the anionic nature. This work aims to check the possible micellar properties of protic ionic liquids formed from a Brønsted acid−base reaction and propose a new mathematical method to verify the ionic liquids self-aggregation. The influences of structural variations in their properties are important to modulate the properties and therefore their applications. The ionic liquids tested are hydroxyethyl amine, N-methyl ethanolamine cations, bis(2hydroxyethyl) amine, and C2 to C5 anions based on carboxylic

1. INTRODUCTION Ionic liquids (ILs) are organic salts that are liquid at room temperature.1−6 These have been widely used as solvents, contribute to the environment as they do not give off gas responsible for the greenhouse effect, and can be used in organic reactions, chromatography, and homogeneous catalysis. The number of applications for ILs continues to grow exponentially.4,7 In the latest years, the aggregate properties and interfacial behavior of amphiphilic ionic liquids have received a lot of attention because of their potential. In recent years, ILs have been used in polymer science, mainly as polymerization media in several types of polymerization processes.8−11 The work of Guerrero-Sanchez10 revealed that aqueous solutions of ionic liquids can be used as a means of reactions and produce better control of particle size than some processes currently used in the industry. The authors reinforce that ionic liquids based on ammonium cations can act as stabilizers of colloidal suspensions. Therefore, as scientific advances continue, it is necessary to investigate micellar properties of other ionic liquids in aqueous solution.12−14 The literature reviews relate a few works to the determination of micellar properties of protic ionic liquids. Anouti et al.15 examined aggregate behavior of the length of alkyl chains (n = C5 to C8) for conductivity measured with a tensiometer and found that the critical micelle concentration (cmc) decreases for the families studied (pyrrolydynium/imidazolium) by increasing the length of the chain. This behavior has been interpreted, according to the authors, in terms of a balance between the forces that overcome the van der Waals and favor the formation of aggregates. In a previous work of our group, Alvarez et al.16 via NMR spectra determined self-diffusion coefficients of ionic liquid 2-hydroxy ethylammonium oleate, the results of which © XXXX American Chemical Society

Received: December 2, 2017 Accepted: March 19, 2018

A

DOI: 10.1021/acs.jced.7b01053 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Chemicals Used in the Present Study

a

CAS number

chemical name

supplier

purity (mol %)

141-43-5 90367-28-5 109-83-1 64-19-7 79-09-4 107-92-6 109-52-4

2-hydroxyethylamine bis(2-hydroxyethyl)amine N-methylethanolamine acetic acid propionic acid N-butyric acid pentanoic acid 2-(hydroxy)ethylammonium acetate 2-HEAA 2-(hydroxy)ethylammonium propionate 2-HEAB 2-(hydroxy)ethylammonium butanoate 2-HEAPr 2-(Hydroxy)ethylammonium pentanoate 2-HEAP Bis(2-hydroxyethyl)ammonium acetate m-2HEAA Bis(2-hydroxyethyl)ammonium propionate m-2HEAPr Bis(2-hydroxyethyl)ammonium butanoate m-2HEAB Bis(2-hydroxyethyl)ammonium pentanoate m-2HEAP N-methyl-2-hydroxy-ethylammonium acetate BHEAA N-methyl-2-hydroxy-ethylammonium propionate BHEAPr N-methyl-2-hydroxy-ethylammonium butanoate BHEAB N-methyl-2-hydroxy-ethylammonium pentanoate BHEAP

Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Vetec Vetec Vetec Vetec synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized

>98 >98 >98 >99 >99 >99 >99 >98 >98 >98 >98 >98 >98 >98 >98 >98 >98 >98 >98

water (ppm)

verification methoda

≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000 ≤1000

NMR, FT-IR NMR, FT-IR NMR, FT-IR NMR, FT-IR NMR, FT-IR NMR, FT-IR NMR, FT-IR NMR NMR NMR NMR NMR NMR NMR NMR NMR NMR NMR NMR

NMR, nuclear magnetic resonance; FT-IR, Fourier transform infrared spectroscopy.

was then washed with deionized water to remove any adhering material and dried to preserve the conductivity before the next measurement. Deionized pure water is a poor electrical conductor with a conductivity of 0.013572 mS/cm. 2.3. New Mathematical Method. The critical micelle concentrations (cmc) in IL/water mixtures were determined by a nonlinear parameter estimation of a proposed unified equation. The proposed fitting equation, F(x) was derived from two arbitrary linear equations, f1(x) and f 2(x), and a smooth regularization function, g(x).

acids (acetate, propionate, and butyrate pentanoate) forming 12 different ionic liquids in aqueous solution.

2. EXPERIMENTAL SECTION 2.1. Preparation of Protic Ionic Liquids. The hydroxyethyl amine, N-methyl ethanolamine and bis(2-hydroxyethyl) amine were obtained from Aldrich with 0.98% mass fraction of purity; the organic acids were obtained from Vetec with a purity greater than 0.99%. These compounds were used as received. The ILs used in this work were prepared from stoichiometric amounts of amines and organic acids using the methodology detailed in the work by Alvarez et al.21 These substances were used with no further purification, and further material characteristics are given in Table 1. The amine was placed in a glass flask fitted with a condenser, a temperature sensor PT-100 temperature control, and a funnel. The apparatus was fitted in an ice bath to keep the reaction temperature below 283.15 K, since the reaction is exothermic. The organic acid was added drop by drop on the balloon with a bar magnet at a 450 rpm agitation rate, applied in order to improve the shock between the reagents, allowing the reaction to complete. The reaction was allowed to rest for 24 h at room temperature in order to obtain a viscous liquid. The reaction is a simple acid−base neutralization of Brønsted forming an ionic liquid. Then, under high vacuum (10−4 Pa) the ILs were totally dried, and the structure was confirmed by FTIR. The water content was determined with a Karl Fisher coulometer, and a mass fraction of water less than 1% was indicated. 2.2. Conductivity Measurements. Conductivity measurements were performed with a hand-held mCA-150P manufactured by Tecnopon with a calibrated cell constant of 1.1 cm −1. The temperature was monitored by a thermometer; the conductivity cell was first set to zero in air followed by calibration with a standard solution prior to the sample being measured with a Tecnopon MS instrumentation solution with 146 mS/cm conductivity. The temperature of the oven was kept constant at 293 ± 1 K. The solutions molar concentration of ionic liquids always was corrected to account for the contribution of the pure solvent present in the ionic liquid prepared. The conductivity cell

f 1(x) = ax + b

(1)

f 2(x) = c(x − d) + f 1(d) = cx + (ad + b − cd)

(2)

⎡ ⎡ (x − d ) g (x) = ⎢.5 + .5⎢ ⎢ ⎢ (x − d)2 + (x − x )2 (ξ)2 ⎣ ⎣ max min

⎤⎤ ⎥⎥ ⎥⎥ ⎦⎦ (3)

This regularization function assumes values close to zero, for values of x lower than d, and assumes values closes to 1, for values of x greater than d. The proposed fitting equation is then assembled in the following manner. F(x) = f 1(x)[1 − g (x)] + f 2(x)[g (x)] = ax + b + (c − a)(x − d)[g (x)]

(4)

22−24

In other works, the CMC determination was done by independently fitting two linear equations to selected experimental points, with two parameters being estimated in each regression, hence, with a total of four parameters being estimated. Linear regressions were performed with one set of data in the lower concentration region, and the other set in the higher concentration region, and the CMC was determined by the interception value between the two lines. This new approach eliminates the subjectivity of selecting experimental points for different independent linear regression. All the set of data is utilized in the estimation procedure of parameters from a single nonlinear equation. The equation B



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contains four parameters, namely, a which represents the slope of the lower concentration region, b which represents the measured variable at zero concentration, c which represents the slope of the higher concentration region, and d which represents the CMC value. It should be noted that through this approach, the lower and higher concentration regions are automatically defined and remove totally the experimenter subjectivity. In addition, the parameter b was assumed fixed as the average measured value for water conductivity at zero IL concentration (0.013572 mS/cm). Therefore, three parameters were estimated, utilizing data from both concentration regions simultaneously. In addition, this methodology allows confidence intervals for the estimated CMC values to be calculated, based on the quality of the fit. Confidence region intervals are very important for comparisons between CMC obtained for different ILs or in different works, as they will define if it can be safely assumed that different values for the estimated CMC are due to different properties of the substances, or may just be the result of experimental fluctuations. The estimation procedure in this work utilized the leastsquares objective function, by comparison of measured and predicted conductivity values for different concentrations.

where H is the Hessian matrix, given by

Hi , j =

∂ 2Fobj ∂αiαj

(8)

Nexp

Fobj( α) = ∼

∑ (yei − yc (xi , ∼α))2 i=1

(5)

Figure 2. Conductivity of {BHEAP + water} solutions at 293 K as a function of concentration.

α is the set of parameters for estimation, xi is the concenwhere ∼ tration measurements, yie is the conductivity measurements, and yic is calculated conductivities. Nexp stands for number of experimental points and Npar stands for number of estimated parameters. Confidence intervals were calculated by performing a t-Student test, with a 95% level of significance. A consistent estimation for experimental variance can be inferred from the estimation square residuals: 2

σy =

Table 2. Critical Micelle Concentration (m/103 mol·kg−1) of Aqueous Solutions of Ionic Liquids, Using New Method to 293 K and 0.1 MPaa ionic liquids 2-HEAA

(6)

V = 2σy 2H −1 ≈

2-HEAP

146.2 172.4 188.0

79.6 98.5 107.2

cmc +

166.8 191.1 212.4

102.6 169.2 253.8

cmc +

162.4 191.1 219.8 BHEAA

95.6 169.2 242.9 BHEAPr

148.6 172.4 196.2 BHEB

84.1 98.5 112.8 BHEAP

131.2 155.1 171.1

119.8 141.1 183.2

111.4 117.0 126.2

ST

The estimated parameter variance matrix is given by ≈

2-HEAB FH

Fobj Nexp − Npar

2-HEAPr

(7)

cmc + cmc +

cmc + cmc +

FH 123.1 132.0 139.9 ST 120.4 132.0 143.6 m-2HEAA FH 147.8 180.4 204.1 ST 147.3 180.4 213.6

129.9 155.1 180.3 m-2HEAPr

105.1 141.1 183.1 m-2HEAB

106.8 117.0 127.2 m-2HEAP

158.2 177.8 190.1

108.8 123.5 135.9

121.1 139.9 158.8

162.5 177.8 193.1

104.6 123.5 142.3

113.1 139.9 166.7

a

Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, expanded uncertainties are U(m) = 1.10−3 mol·kg1− (95% level of confidence). Notation: cmc, critical micellar concentration; ±, confidence region; FT − Fisher Test; ST, Student Test.

Figure 1. Conductivity of {m-2HEAPr + water} solutions at 293 K as a function of concentration. C



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And finally, limit parameter values are calculated by αlim = α ± t ‐Student 2.5%σα

for 12 protic ionic liquids based on ammonium cation in mixtures with water using the proposed method. When an ionic liquid is dissolved in water, the presence of the hydrophobic part causes a distortion in the water structure, which increases the free energy of the system. In this result the entropy system decreases due to the structuring of water molecules around the hydrophobic chain (“hydrophobic hydration”) and to the reduction in degrees of freedom of the hydrophobic chain.26−29 However, to minimize the free energy of the system, the molecules of ionic liquids adsorb in the air/water interface. In ILs adsorbed, their hydrophobic chains are facing out of the solution and the hydrophilic groups remain in the aqueous interface. The energy decreases due to the gain in entropy by releasing the water of hydration and by the replacement of water molecules by molecules of ionic liquids on the interface. Alternatively, they can also suffer other processes in order to reduce the energy, when the concentration of surfactants in the solution is increased, the molecules present within the solution come together forming micelles. As the work to take a surfactant molecule to the interface is smaller than that corresponding to one molecule of water, the surfactant presence decreases the work needed for a larger interfacial area resulting in a reduction of surface tension.22,30−33

(9)

The objective function minimization given was performed by the particle swarm optimization algorithm (PSO). PSO25 is a heuristic algorithm, consisting of random evaluations of the objective function in an given parameter search region, a determinist and a random weight term for guidance of consecutive evaluations. This optimization methodology allows the abstention of a more reliable confidence interval, which is not necessarily symmetrical. All parameter value sets, which during the stochastic sampling, yield an objective function with a value lower than a limit, are considered as a part interval. This limit is calculated from a Fisher test with Npar and Nexp − Npar degrees of freedom, and, as defined for the t-Student test, with a 95% level of significance. ⎛ ⎞ Npar ⎟Fisher95% Flimit = Fobj⎜⎜1 + Nexp − Npar ⎟⎠ ⎝

(10)

3. RESULTS AND DISCUSSION This paper proposes a mathematical method for the objective determination of CMC values from conductivity experiments and presents results of determination of critical micelle concentration

Table 3. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and Temperatures (T) at Ambient Pressure 0.1 MPa (p)a m-2HEAA

2HEAA 3

m/10 mol·kg

−1

σ/ mS·cm

−1

3

m/10 mol·kg

−1

BHEAA −1

σ/ mS·cm

3

m/10 mol·kg

−1

σ/ mS·cm−1

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

24.10 47.96 74.52 99.82 126.74 151.85 177.81 202.54 228.46 252.12 275.46 297.71 319.93 340.41 361.46 381.08 400.30 418.42 435.90 452.65 464.20 479.67 494.26 508.55 522.10 535.12 547.31 559.42 570.52

20.15 39.83 57.74 74.16 90.15 105.73 121.35 135.56 148.47 162.08 174.28 186.74 200.36 215.74 232.55 250.23 269.05 286.75 303.21 318.90 333.66 347.58 360.85 385.54 407.49 427.85 446.31 462.69 477.43

1.38 2.74 4.00 5.12 6.28 7.37 8.47 9.50 10.62 11.58 12.32 13.31 14.18 14.87 15.67 16.39 17.15 17.72 18.30 18.66 18.99 19.40 19.92 20.41 20.86 21.28 21.69 22.28 22.67

1.30 2.62 3.59 4.50 5.39 6.18 7.02 7.75 8.35 9.00 9.58 10.19 10.77 11.42 12.13 12.89 13.68 14.37 14.35 14.80 15.64 16.07 16.13 17.50 18.65 19.29 19.84 20.33 20.77

21.02 41.30 64.89 86.42 109.98 133.00 156.60 178.40 201.51 223.31 245.90 267.06 288.52 308.34 328.53 347.10 365.82 383.19 400.41 416.33 432.24 447.16 461.75 475.12 488.07 500.53 512.86 524.35 535.54

22.29 45.56 69.82 92.90 118.18 144.20 169.99 193.16 217.56 240.35 263.33 285.33 307.58 328.54 349.50 368.90 388.60 406.83 424.79 441.66 458.34 473.78 488.98 503.21 517.22 530.21 543.61 556.07

1.03 1.89 2.99 3.80 4.71 5.51 6.37 7.15 7.90 8.70 9.47 10.14 10.80 11.41 12.04 12.60 13.17 13.71 14.21 14.64 15.08 15.51 15.94 16.37 16.81 17.25 17.61 17.97 18.26

0.92 1.85 2.99 3.87 4.81 5.74 6.64 7.49 8.22 8.92 9.66 10.32 11.09 11.61 12.20 12.75 13.31 13.83 14.32 14.73 15.15 15.60 16.07 16.49 16.80 17.03 17.34 17.58

17.97 35.39 53.69 71.32 90.23 108.43 126.40 145.84 164.08 180.86 198.35 213.31 230.75 246.03 261.58 276.00 290.42 304.20 317.48 329.84 342.20 354.23 365.43 376.47 386.77 396.73 406.47 415.54 424.48

15.79 32.69 51.65 69.43 88.22 106.33 125.47 143.33 161.99 179.33 197.19 213.44 230.26 245.78 261.46 276.19 290.92 304.42 317.82 330.25 342.50 354.01 365.45 376.00

0.90 1.62 2.36 3.18 3.85 4.53 5.51 6.12 6.65 7.13 7.62 8.04 8.38 8.77 8.61 8.93 9.26 9.57 10.15 10.42 10.71 10.97 11.21 11.45 11.67 11.88 12.10 12.40 12.69

0.77 1.40 2.10 2.90 3.56 5.07 5.61 6.07 6.60 7.05 7.50 7.87 8.33 8.70 8.99 9.42 9.68 9.98 10.29 10.40 10.80 11.07 11.34 11.56

Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) = 1.10−3 mol·kg−1 (95% level of confidence). a

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Figures 1 and 2 show the behavior of the ionic conductivity of the liquid solutions, studied in order to obtain the critical micelle concentration (CMC) of each binary system. You can see in the figures the change of ownership with the increased concentration of N-methyl-2-hydroxyethylammonium propionate {m-2HEAPr} and bis(2-hydroxyethyl) ammonium pentanoate {B2HEAP}, that point where there is a change in the slope of the line, which is called the cmc. Details about the proposed method can be seen in section 3, where the variables and fitted parameters equation used to represent the conductivity of ionic liquids in aqueous solution are described in detail. The deviations of the fitting equation are less than 1%. Tables 2 to 6 summarize values of concentration in which the phenomenon (CMC) occurs. This can be realized with ionic liquids based on carboxylic acids, which would be governed by a particular structural factor considering the number of carbon atoms in the chain, methyl, or hydroxyl groups and are not sufficient for property control. In addition, entropic factors are highly related to this property, that is, the decrease in entropy due

to the structuring of water molecules around the hydrophobic IL sector is the most influential factor for the organization. Perhaps, by structural similarity and similar solubility levels of the compounds studied, there is the concentration proximity value on which the phenomenon of critical micelle occurs. It is important to notice that with the series of ionic liquids in this work, all feature values with physical meaning, that is, the estimated parameter d of the proposed model, feature significant values and never show negative values.

4. CONCLUSION The ionic liquid micelle formation in water was investigated for ionic liquids based on the ammonium cation. The conductivity of ionic liquids solutions with increasing concentration was studied in this work with a new methodology to determine the CMC value. Our results indicate that the reduction in the carbonic chain of anion promotes the process of formation of micelles due to differences in solubility in the solvent. This work also shows that the formation of aggregates with protic ionic liquids is

Table 4. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and Temperatures (T) at Ambient Pressure 0.1 MPa (p)a m-2HEAPr

2HEAPr 3

m/10 mol·kg

−1

σ/ mS·cm

−1

3

m/10 mol·kg

−1

BHEAPr −1

σ/ mS·cm

3

m/10 mol·kg

−1

σ/ mS·cm−1

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

17.86 34.91 54.16 72.80 92.90 112.15 132.24 150.40 169.20 188.05 206.69 232.80 253.17 272.87 290.49 307.40 323.71 338.79 353.43 366.85 379.83 391.71 403.20 413.77 423.98 535.12 547.31 559.42 570.52

22.00 44.47 68.41 91.26 113.70 137.34 159.37 182.23 203.82 226.27 247.19 268.04 287.72 307.35 325.08 342.68 359.37 375.54 390.49 405.50 419.47 433.40 446.50 459.06 470.89 482.48

1.07 1.98 3.12 4.00 4.85 5.74 6.58 7.40 8.21 8.97 9.82 10.84 11.64 12.39 13.03 13.68 14.26 14.81 15.32 15.79 16.26 16.68 17.06 17.43 17.79 18.16 18.55 18.90 19.25

1.16 2.18 3.38 4.30 5.21 6.12 6.95 7.80 8.45 9.21 9.91 10.58 11.22 11.84 12.38 12.92 13.41 13.92 14.34 14.77 15.14 15.53 15.87 16.17 16.45 16.72

19.26 37.49 57.27 75.96 95.70 114.17 133.49 151.90 170.71 184.51 202.93 220.04 237.48 253.47 269.63 284.96 300.22 314.17 328.23 341.30 353.85 365.80 377.47 388.41 399.18 409.22 419.02 428.27 437.19 445.66 453.91 461.66 469.20 475.88

19.74 37.70 57.22 76.10 96.17 115.20 135.00 154.25 171.80 189.85 207.12 224.35 240.64 257.11 272.20 287.53 301.87 316.21 329.34 342.40 354.47 365.97 377.44 388.11 398.62 408.30 418.01 427.11 436.10 444.50 452.71

1.09 1.96 2.96 3.75 4.56 5.28 6.01 6.70 7.37 7.85 8.49 9.01 9.55 10.02 10.49 10.91 11.29 11.68 12.05 12.40 12.73 13.04 13.25 13.62 13.89 14.13 14.36 14.58 14.87 15.10 15.35 15.56 15.78 15.94

1.04 1.92 2.96 3.65 4.47 5.19 5.96 6.68 7.25 7.98 8.75 9.42 9.97 10.29 10.80 11.25 11.70 11.61 12.26 12.68 13.13 13.50 13.86 14.09 14.37 14.69 14.98 15.27 15.49 15.75 16.02

15.50 31.83 48.90 65.27 80.46 97.48 113.58 130.51 146.35 162.24 177.56 193.46 208.08 223.01 237.01 249.95 263.22 275.63 287.91 299.35 310.60 321.05 331.72 341.47 351.11 360.17 369.11 377.42 385.63 393.35 400.86 407.90 414.84

14.87 31.59 48.81 64.92 82.14 98.89 115.88 132.44 149.54 165.12 181.35 196.58 212.07 226.36 240.77 254.17 267.73 280.03 292.24 303.62 314.86 325.46 335.69 345.43 354.99 363.99 372.60 380.78 388.54 395.99 403.18 409.85 416.49 422.72

0.73 1.39 2.02 2.77 3.29 3.84 4.36 4.87 5.36 6.04 6.48 6.90 7.27 7.64 7.98 8.29 8.72 9.08 9.33 9.57 9.80 10.01 10.22 10.41 10.60 10.77 10.94 11.09 11.34 11.53 11.74 11.91 12.07

0.66 1.33 1.95 2.66 3.23 3.78 4.27 4.76 5.23 5.68 6.13 6.54 6.94 7.02 7.21 7.23 7.86 8.14 8.34 8.60 9.06 9.23 9.46 9.67 9.87 10.08 10.30 10.49 10.51 10.70 10.86 10.94 11.11 11.24

Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) = 1.10−3 mol·kg−1 (95% level of confidence). a

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Table 5. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and Temperatures (T) at Ambient Pressure 0.1 MPa (p)a m-2HEAB

2HEAB m/103 mol·kg−1

σ/ mS·cm−1

m/103 mol·kg−1

BHEAB σ/ mS·cm−1

m/103 mol·kg−1

σ/ mS·cm−1

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

20.70 41.50 62.47 82.83 104.87 125.81 147.57 168.07 188.84 208.72 228.41 246.85 265.38 282.46 300.12 316.47 332.65 347.54 362.24 375.81 389.41 402.08 414.42 425.94 437.35 447.96 458.39 468.10 477.53 486.43 494.98 503.24

18.55 35.07 56.78 76.51 97.13 119.01 140.74 162.84 184.02 205.48 225.13 244.84 262.64 280.94 297.97 315.30 331.00 346.75 361.32 375.94 389.20 402.29 414.48 423.11 434.40 444.92 455.37 465.08 474.59 483.51 492.22 500.51 508.55 516.00 523.07

1.07 1.96 2.95 3.72 4.49 5.11 5.85 6.49 7.11 7.64 8.10 8.57 9.00 9.40 9.82 10.20 10.56 10.88 11.21 11.49 11.78 12.04 12.28 12.51 12.75 12.95 13.16 13.34 13.55 13.76 13.95 14.11

0.92 1.63 2.64 3.38 4.10 4.85 5.63 6.37 7.09 7.70 8.34 8.94 9.46 9.94 10.41 10.86 11.22 11.66 12.04 12.32 12.69 12.97 13.24 13.41 13.65 13.87 14.09 14.27 14.46 14.63 14.84 15.03 15.21 15.36 15.52

18.05 35.16 53.97 70.90 94.24 108.51 127.48 145.53 163.81 180.70 198.19 214.40 230.97 246.38 261.59 275.77 289.91 303.18 316.24 328.35 340.24 351.40 362.25 372.56 382.63 391.74 402.17 411.46 420.14 428.43 436.79 444.55

17.98 35.77 55.31 74.33 94.07 112.20 131.56 149.61 168.30 185.95 203.48 220.28 237.03 252.45 267.89 282.41 297.05 310.60 323.99 332.14 343.83 355.47 366.50 377.36 387.47 397.46 406.84 415.98 424.50 432.96

0.90 1.66 2.57 3.18 3.89 4.53 5.19 5.81 6.41 6.96 7.50 8.01 8.70 9.12 9.54 9.94 10.30 10.65 11.00 11.31 11.63 11.91 12.19 12.44 12.67 12.86 13.21 13.50 13.77 14.02 14.27 14.50

0.77 1.42 2.07 2.84 3.46 4.03 4.86 5.38 5.77 5.97 6.51 6.94 7.25 7.64 7.82 8.21 8.62 9.08 9.50 9.80 10.02 10.22 10.47 10.46 10.70 10.97 11.17 11.41 11.61 11.82

14.43 30.59 47.18 63.11 80.77 96.98 114.60 130.69 147.95 163.76 180.21 195.23 210.60 224.59 238.43 251.38 264.41 276.63 288.65 299.76 311.01 321.44 331.71 341.19 350.50 359.26 367.85 375.81

16.09 31.61 48.51 64.01 81.76 97.05 113.92 129.83 146.40 161.39 177.05 191.79 206.42 220.08 233.62 246.59 259.56 271.16 283.02 294.05 304.81 314.84 324.72 333.97 343.01 351.51 359.87 367.68

0.41 0.77 1.15 1.49 1.85 2.32 2.67 2.97 3.28 3.55 3.83 4.08 4.34 4.56 4.78 4.96 5.16 5.28 5.42 5.58 5.72 5.86 6.00 6.11 6.24 6.34 6.46 6.56

0.47 0.84 1.22 1.55 1.89 2.35 2.68 2.98 3.24 3.50 3.72 3.95 4.20 4.40 4.60 4.80 4.98 5.13 5.25 5.40 5.56 5.71 5.83 5.96 6.07 6.19 6.29 6.39

a Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) = 1.10−3 mol·kg−1 (95% level of confidence).

Table 6. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and Temperatures (T) at Ambient Pressure 0.1 MPa (p)a m-2HEAP

2HEAP 3

m/10 mol·kg

−1

−1

σ/ mS·cm

3

m/10 mol·kg

−1

BHEAP σ/ mS·cm

−1

3

−1

m/10 mol·kg

σ/ mS·cm−1

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

19.13 37.18 56.21 74.57 94.98 113.49 133.64 151.97 171.77 189.91 206.68 223.96 240.04

19.18 37.81 58.01 77.59 99.26 118.75 140.16 159.40 179.61 198.14 217.36 234.78 252.87

1.08 1.90 2.60 3.09 3.65 4.12 4.80 5.26 5.78 6.25 6.61 7.01 7.39

0.68 1.26 1.76 2.44 2.96 3.44 3.93 4.39 4.83 5.23 6.64 5.97 6.37

14.62 30.93 48.74 64.76 82.67 99.39 116.98 133.04 148.78 162.95 177.91 191.56 205.78

17.05 32.18 49.10 65.59 81.09 97.93 115.87 132.60 150.73 166.82 183.76 199.44 215.25

0.55 1.08 1.61 2.04 2.68 3.12 3.65 4.08 4.49 4.86 5.24 5.26 5.58

0.64 1.16 1.68 2.15 2.79 3.28 3.75 4.20 4.70 5.12 5.57 5.95 6.34

13.96 27.42 42.10 55.79 60.70 83.28 96.05 109.53 122.38 135.85 148.38 160.78 172.66

11.38 24.31 39.23 52.24 67.05 80.75 95.53 109.18 123.99 137.24 150.55 163.21 175.86

0.62 1.13 1.65 2.09 2.69 3.10 3.30 4.08 4.45 4.79 5.13 5.44 5.72

0.49 0.98 1.49 1.91 2.38 2.93 3.35 3.75 4.16 4.49 4.85 4.98 5.27

F



Article

Table 6. continued m-2HEAP

2HEAP m/103 mol·kg−1

σ/ mS·cm−1

m/103 mol·kg−1

BHEAP σ/ mS·cm−1

m/103 mol·kg−1

σ/ mS·cm−1

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

test 1

test 2

256.45 272.04 287.53 301.98 316.49 329.94 343.45 356.08 368.53 379.98 391.41 401.97 412.57 422.09 431.63 440.43

269.72 286.67 302.36 318.08 332.87 347.40 360.82 374.38 386.58 398.76 410.12 421.46 431.79 442.11 451.73

7.76 8.09 8.44 8.75 9.04 9.30 9.57 9.83 10.10 10.32 10.53 10.73 10.93 11.10 11.30 11.44

6.69 7.04 7.34 7.59 7.86 8.12 8.32 8.55 8.76 8.95 9.17 9.25 9.40 9.57 9.71

219.67 233.65 246.74 259.98 272.31 284.82 296.49 307.92 318.79 339.59 349.42 358.48 367.53 376.02 384.36 392.07 399.74 406.92 444.55

229.72 244.66 258.40 272.12 285.08 297.63 309.60 321.39 332.13 342.81 352.67 362.52 371.63 380.63 389.04 397.26

5.93 6.24 6.55 6.85 7.11 7.39 7.55 7.89 8.11 8.35 8.54 8.76 8.93 9.14 9.25 9.25 9.25 9.73 9.91

6.69 7.06 7.39 7.67 7.95 8.22 8.48 8.74 8.96 9.18 9.40 9.60 9.79 9.99 10.15 10.31

184.40 194.73 205.91 216.36 226.01 235.85 245.09 254.06 262.47 270.31 278.33 285.33 292.90 299.80 306.52 312.88 319.14 324.94 330.68 336.02 341.31

187.86 199.94 211.26 222.56 232.89 242.65 252.30 261.96 270.93 279.69 288.20 296.37 303.97 311.40 318.43 325.48 331.70 337.85 343.66 349.34 354.60

5.97 6.12 6.35 6.56 6.77 6.97 7.09 7.27 7.44 7.60 7.76 7.90 8.04 8.18 8.30 8.42 8.53 8.68 8.80 8.93 10.37

5.51 5.78 6.02 6.20 6.42 6.63 6.82 7.01 7.17 7.35 7.50 7.66 7.81 7.94 8.08 8.19 8.34 8.47 8.58 8.70 8.82

a Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) = 1.10−3 mol·kg−1 (95% level of confidence).

Ionic Liquids Based on Stearate Anion. Fluid Phase Equilib. 2014, 376, 132−140. (2) Santos, D.; Bamufleh, H. S.; Uslu, H. Prigogine-Flory-Patterson Evaluation of Systems with Ionic Liquids + Water or Methanol: A Study of Specific Interactions. J. Mol. Liq. 2018, 253, 23−27. (3) Pinto, R. R.; Santos, D.; Mattedi, S.; Aznar, M. Density, Refractive Index, Apparent Volumes and Excess Molar Volumes of Four Protic Ionic Liquids + Water at T = 298. 15 and 323. 15 K. Braz. J. Chem. Eng. 2014, 32, 671−682. (4) Santos, D.; Costa, F.; Franceschi, E.; Santos, A.; Dariva, C.; Mattedi, S. Synthesis and Physico-Chemical Properties of Two Protic Ionic Liquids Based on Stearate Anion. Fluid Phase Equilib. 2014, 376, 132−140. (5) Santos, D.; Góes, M.; Franceschi, E.; Santos, A.; Dariva, C.; Fortuny, M.; Mattedi, S. Phase Equilibria for Binary Systems Containing Ionic Liquid with Water or Hydrocarbons. Braz. J. Chem. Eng. 2015, 32, 967−974. (6) Santos, D.; Santos, M.; Franceschi, E.; Dariva, C.; Barison, A.; Mattedi, S. Experimental Density of Ionic Liquids and Thermodynamic Modeling with Group Contribution Equation of State Based on the Lattice Fluid Theory. J. Chem. Eng. Data 2016, 61, 348−353. (7) Á lvarez, V. H.; Dosil, N.; Gonzalez-Cabaleiro, R.; Mattedi, S.; Martin-Pastor, M.; Iglesias, M.; Navaza, J. M. J. M. Brønsted Ionic Liquids for Sustainable Processes: Synthesis and Physical Properties †. J. Chem. Eng. Data 2010, 55, 625−632. (8) Biedró, T.; Kubisa, P. Ionic Liquids as Reaction Media for Polymerization Processes: Atom Transfer Radical Polymerization (ATRP) of Acrylates in Ionic Liquids. Polym. Int. 2003, 52, 1584−1588. (9) Kubisa, P. Application of Ionic Liquids as Solvents for Polymerization Processes. Prog. Polym. Sci. 2004, 29, 3−12. (10) Guerrero-Sanchez, C.; Erdmenger, T.; Šereda, P.; Wouters, D.; Schubert, U. S. Water-Soluble Ionic Liquids as Novel Stabilizers in Suspension Polymerization Reactions: Engineering Polymer Beads. Chem. - Eur. J. 2006, 12, 9036−9045. (11) Kubisa, P. Ionic Liquids as Solvents for Polymerization ProcessesProgress and Challenges. Prog. Polym. Sci. 2009, 34, 1333−1347.

similar to that of other surfactants such as omim cl and SDS. Consequently, the results are compatible with the possibility of solvophobic-type interactions within the solvent, being one of those responsible for the process of self-aggregation along with entropic and lipophilic factors and when water molecules are organized along the hydrophobic region of ionic liquids.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b01053. Mathematical model in python and tutorial video (ZIP)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; dheiver.santos@ gmail.com. ORCID

Dheiver Santos: 0000-0002-8599-9436 Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS The author wishes to express his sincere gratitude to his ́ de colleagues at the Tiradentes University Center and Mauricio Nassau University Center, Professors Iuri Segtovich (UFRJ), Silvana Mattedi (UFBA) and Edilson Ponciano (UNIT) for all their support.

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REFERENCES

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